Polypropylene-based graft copolymers are useful as compatibilizers for a variety of polymer blends containing polypropylene. These blends include those where the composition is entirely composed of polyolefins and those where an inorganic filler such as clays or glass fiber is also present. In particular, these inventions are directed to the formation of these graft polymers to form propylene rich components that contain isotactic polypropylene crystallinity. These elastic polymers may be used as blend components as well as adhesion promoters between polyolefins and substrates such as glass, metal and engineering plastics such as polyamides. It is however acknowledged that these grafted polyolefins, particularly those that have a predominance of propylene in their composition and have most of the propylene in predominantly isotactic configuration have poor elastic properties.
Graft reactions of polyolefins consisting largely of polypropylene is known via solution reactions, gas phase surface modification. However, the most common processes involve melt processing procedures such as single or multiple screw extruders, rubber masticators, Banbury processors, Brabender processors, roll-mills and the like, include well-known technology and are widely reported in the technical literature. Similarly, post-graft reactions with the graft polymers are also widely reported in all of the media and procedures shown above. Thus, the graft reaction of unsaturated carboxylic acid or carboxylic acid derivatives with thermoplastic polymers or low molecular weight chemicals capable of subsequent chemical reaction for use in such as lubricating oil compositions or thermoplastic blend compositions has become an important field of ongoing development.
Polypropylene grafting with unsaturated monomers including maleic anhydride is well documented in the literature (see S. B Brown, in Reactive Extrusion, Chapter 4, Polymer Processing Institute, 1992). U.S. Pat. No. 5,439,974 addresses adhesive blends suitable for adhesion to one or more polypropylene substrates consisting essentially of a mixture of an impact copolymer and a graft reaction product of a propylene polymer and a carboxylic acid or derivative thereof. The polymeric backbone which is grafted is an impact copolymer defined as a mixture of polypropylene and ethylene/propylene copolymer. The impact copolymers in U.S. Pat. No. 5,439,974 are mixtures prepared by a multistage polymerization process and are usually identified as reactors TPOs or heterophasis polypropylene (column 3, line 61 to column 4, line 7).
U.S. Pat. No. 5,451,639 addresses propylene copolymers grafted with ethylenically unsaturated carboxylic acids or carboxylic acid derivatives and consisting of a random copolymer containing from 0.1 to 15 weight % of copolymerized C2 or C4 to C10 1-alkenes. Further examples of the grafting of unsaturated carbonyl compounds to polypropylene and copolymers containing very large amounts of propylene are shown in the following publications that are fully incorporated by reference. In Modification of Polypropylene with Maleic Anhydride, Hogt, ANTEC '88 Proceedings of the 46th Annual Technical Conference, Atlanta, 18-21 April 1988, p.1478-80, Maleic Anhydride Grafting of Polypropylene with Organic Peroxides, and Callais et al, ANTEC '90 Plastics in the Environment: Yesterday, Today and Tomorrow, Conference Proceedings, Dallas Tex., 7th-11th May 1990, p. 1921-3, Carbon 13 NMR Study of the Grafting of Maleic Anhydride onto Polyethylene, Polypropylene, and Ethene-Propene Copolymers, the maleation of isotactic polypropylene homopolymers is taught.
As shown in the literature above, the functionalization of polyolefins which contain predominantly large amounts of propylene and contain isotactic crystallinity is of importance. However, none of these publications address the formation of a essentially propylene copolymer with most of the propylene in isotactic configuration which is grafted with maleic anhydride or other similar unsaturated carbonyl compound which is elastic, soft and has very low levels of crystallinity.
In addition, U.S. Pat. No. 3,862,265 addresses degradation in molecular weight to achieve narrow molecular weight distribution, and optional free-radical initiated graft reaction of unsaturated monomers with, for example, ethylene-propylene copolymer by use of melt processing procedures in an extruder reactor. Intensive mixing of free radical initiator and graft reactants with molten polymers is achieved by the use of either decompression zones or thin film zones in the extruder. For additional background, see also EP 0 770 641 A; GB 1 040 539 A; GB 879 195 A; EP 0 767 182 A; GB 1 531 188 A; GB 1 578 049 A; U.S. Pat. No. 4,780,228 A; GB 2 022 597 A; U.S. Pat. No. 4,159,287 A; EP 0 964 011 A; U.S. Pat. No. 3,416,990 A; and U.S. Pat. No. 5,504,172.